1. Field of the Invention
The present invention relates to a focal plane shutter for cameras having one or two shutter blades.
2. Description of the Related Art
Two types of focal plane shutters for cameras are known. One includes two shutter blades (a front blade and a rear blade) and the other includes one shutter blade. The former including two shutter blades has been adopted in silver film cameras and digital cameras, while the latter inducing one shutter blade has been adopted only in digital cameras. In the focal plane shutter of either type, each shutter blade is constituted by two arms individually pivoted at one end on a surface of a shutter base plate on a blade chamber side, and at least one blade pivoted on both of the arms.
A driving member for a shutter blade is rotatably mounted to a surface of the shutter base plate outside the blade chamber, and a driving pin thereof is connected to one arm of the shutter blade in the blade chamber. The driving member is rotated by a biasing force of a driving spring to rapidly move the shutter blade in photography, and rotated against the biasing force of the driving spring by a setting member to return the shutter blade to a set state in setting. The driving member deenergizes an electromagnet to start rotation as described above in photography, and a holding configuration of the driving member immediately before the start of rotation includes a locking type configuration and a direct type configuration.
As a typical locking type configuration, a configuration including a shutter blade driving mechanism described in Japanese Utility Model Publication No. 6-24825 and a control mechanism described in Japanese Utility Model Publication No. 4-3301 (a front blade system and a rear blade system are placed in opposite manner in the mechanisms in Japanese Utility Model Publication No. 6-24825 and Japanese Utility Model Publication No. 4-3301), and a configuration described in Japanese Utility Model Publication No. 7-3392. The former configuration includes a releasing member (an opening iron scrap lever 4 and a closing iron scrap lever 7 in Japanese Utility Model Publication No. 4-3301) for releasing a driving member locked by a locking member in photography, and includes a holding member (a first holding lever 10 in Japanese Utility Model Publication No. 4-3301) so that an iron scrap member (iron scraps 4a and 7a in Japanese Utility Model Publication No. 4-3301) mounted to the releasing member is maintained in contact with an iron core member of an electromagnet until a coil of an electromagnet (electromagnet coils 2 and 3 in Japanese Utility Model Publication No. 4-3301) is energized in photography. In the latter configuration, a holding member is not required for maintaining the contact state as described above, and a setting member of a driving member directly acts as the holding member.
On the other hand, a direct type configuration does not include a holding member, a locking member and a releasing member unlike the locking type configuration, and is configured so that an iron scrap member is mounted to a driving member, a setting member maintains the driving member in a set state against a biasing force of a driving spring until a coil of an electromagnet is energized in photography to maintain an iron core member of the electromagnet in contact with the iron scrap member as described in Japanese Patent Laid-Open Nos. 9-304808 and 2001-188279.
In the focal plane shutters having such configurations, having either one shutter blade or two shutter blades, or of either a locking type or a direct type, the electromagnet starts sucking and holding the iron scrap member when the coil of the electromagnet is energized in a stage immediately after a release and immediately before a start of photography as described above. Thus, if a sucked surface of the iron scrap member is tilted with respect to a sucking surface of the electromagnet at the start of energization, and both the surfaces are not in tight contact with each other, a sufficient sucking and holding force by the electromagnet cannot be obtained, and the driving member starts rotation by the biasing force of the driving spring before predetermined timing to cause the shutter blade to start an exposure operation. Thus, in order to always maintain the sucked surface of the iron scrap member in tight contact with the sucking surface of the electromagnet, various methods of improving a mounting configuration of an iron scrap member or an electromagnet have been proposed. Among the proposals, an improvement in a mounting configuration of an iron scrap member to a driving member is described in Japanese Patent Laid-Open Nos. 9-304808 and 2001-188279.
In a configuration described in Japanese Patent Laid-Open Nos. 9-304808 and 2001-188279, an iron scrap member has an iron scrap portion (an iron scrap in Japanese Patent Laid-Open No. 9-304808) at one end of a shaft (an iron scrap shaft in Japanese Patent Laid-Open No. 9-304808), and a flange (a head in Japanese Patent Laid-Open No. 2001-188279) at the other end, and the shaft is loosely fitted in a hole formed in a mounting portion of a driving member. Since the iron scrap member biases the iron scrap portion toward an electromagnet with a spring, the flange is in contact with an edge of a mounting hole formed in the mounting portion of the driving member when the iron scrap portion is not in contact with an iron core member of the electromagnet. If a sucked surface of the iron scrap portion is tilted with respect to a sucking surface of the iron core member when the iron scrap portion is brought into contact with the iron core member of the electromagnet in setting, a center line of the shaft of the iron scrap member is tilted with respect to a center line of the mounting hole so that the sucking surface and the sucked surface are brought into tight contact with each other. At this time, the flange is also tilted, but the edge of the mounting hole interferes with a peripheral portion of the flange to sometimes prevent the flange from being smoothly tilted. In order to prevent this, as specified in drawings of Japanese Patent Laid-Open Nos. 9-304808 and 2001-188279, it is known that the edge of the mounting hole is formed to have an arcuate surface. Besides, as described in Japanese Utility Model Laid-Open No. 56-53310, it is also known that two protrusions (protrusions 23d) are formed with the mounting hole therebetween.
Forming the edge of the mounting hole into such a shape is also desirable for other reasons. Specifically, in terms of production, it is difficult to stop rotation of the driving member at the moment when the iron core member and the iron scrap portion are brought into tight with each other in setting. For this reason, the driving member is actually produced to stop at timing as early as possible after the tight contact state is reliably obtained. Thus, in a setting completion state, the flange of the iron scrap member is placed away from the edge of the hole of the mounting portion as shown in FIG. 3 of Japanese Patent Laid-Open No. 9-304808 and FIG. 2 of Japanese Patent Laid-Open No. 2001-188279. With such a configuration, when the iron scrap member is sucked and held by the iron core member of the electromagnet and then a setting member having maintained the contact state between the members escapes in an initial stage of photography, the driving member is slightly rotated by the biasing force of the driving spring until the edge of the mounting hole abuts the flange of the iron scrap member. When the iron scrap member with the tilted shaft is brought into tight contact with the iron core member in setting as described above, the edge of the mounting hole abuts only part of the peripheral portion of the tilted flange.
When the edge of the mounting hole abuts only part of the peripheral portion of the flange, a force in abutment is not vertically applied to the sucked surface of the iron scrap member but is applied to tilt the sucked surface with respect to the sucking surface. Thus, even while the coil of the electromagnet is energized, the iron scrap member is easily separated from the iron core member of the electromagnet. If the iron scrap member is separated therefrom, the driving member starts an exposure operation with a shutter blade even though not at predetermined timing. In order to prevent this, a suction force by the electromagnet may be increased, which increases the size of the electromagnet or consumption of a battery. Further, the edge of the mounting hole repeatedly abuts part of the peripheral portion of the tilted flange, the edge of the mounting hole is damaged, thereby preventing the tight contact state as described above from being obtained.
On the other hand, with the configuration such that the edge of the mounting hole abuts only part of the peripheral portion of the flange, when the coil of the electromagnet is deenergized, and the driving member starts rotation at predetermined timing, the edge of the mounting hole is brought into contact with the entire surface of the flange, and rattles at that time may affect a stable movement of the shutter blade. Thus, in this view, it is preferable to form the edge of the mounting hole to have the arcuate surface as described in Japanese Patent Laid-Open Nos. 9-304808 and 2001-188279, or form the two protrusions with the hole therebetween as described in Japanese Utility Model Laid-Open No. 56-53310. The mounting configuration of the iron scrap member has been described with the direct type configuration in mind, but the same applies to the locking type configuration described in Japanese Utility Model Publication Nos. 4-3301 and 7-3392. The present invention mainly relates to such a mounting configuration of the iron scrap member.
In the mounting configuration of the iron scrap member described in Japanese Patent Laid-Open Nos. 9-304808 and 2001-188279, the edge of the mounting hole is formed to have the arcuate surface as described above. Thus, this configuration is suitable when the iron scrap member is tilted on a surface parallel to a rotation surface of the driving member. However, when the iron scrap member is tilted on a surface perpendicular to the rotation surface of the driving member, there is little problem if a thickness of the mounting portion (a vertical dimension with respect to the rotation surface) is smaller than a diameter of the flange, but the iron scrap member cannot be suitably tilted if the thickness of the mounting portion is equal to or larger than the diameter of the flange, thereby preventing desired advantages from being sufficiently provided. Comparing FIGS. 1 and 6 in Japanese Patent Laid-Open No. 9-304808 in this view, the diameter of the flange is apparently smaller than the thickness of the mounting portion. Further, in the configuration described in Japanese Patent Laid-Open No. 9-304808, like the configuration of the electromagnet actually implemented, the iron core member is U-shaped and has two magnetic pole portions. Thus, in order to bring a substantially rectangular iron scrap portion into tight contact with the two magnetic pole portions, it is necessary that the iron core member is suitably tiltable in a direction perpendicularly to the rotation surface of the driving member. Also in the mounting configuration of the iron scrap member described in Japanese Utility Model Laid-Open No. 56-53310, the configuration is suitable when the iron scrap member is tilted on one plane, but does not allow the iron scrap member to be suitably tilted in a direction perpendicular to the plane.